I currently have my kid at Fun & Fit in Burbank which is good if they are beginners and you just want them to get a non competitive experience. I also am looking into other gyms at the moment and haven't settled on one yet. But I have learned a little.
Once your child reaches a certain level you'll want to look for a gym that has rated instructors. Getting technique and a strong foundation is important to minimize any chances of injury when they start working on harder tricks.
You'll have to go in speak to the coaches and watch the classes to see which one will meet your needs. Do ask about their background, certification, credentials and philosophy of teaching.